The untreated samples dried in a solar drier showed signs of
spoilage on the second day; those dried directly in the sun
spoiled after three days. It appears that the solar drier
accelerated spoilage because it produced higher air temperatures
(50-70 °C) than sun drying. The spoilage in both cases was
characterized by the development of gas, with a hydrogen sulphide
odour, and excessive dripping and maceration, a sign of impending
putrefaction. Both samples developed greenish and black spots and
a foul smell in three to six days. In addition, the meat
attracted a lot of flies.

The low ERV of the untreated samples40% for those dried
directly in the sun and 10% for those dried in the solar drier,
compared with 96% for the deep-frozen reference
sampleshowed extreme spoilage. The ERV indicates the degree
of proteolytic degradation of the meat, which increases the
water-soluble proteins, thus restricting the ERV [6]. The higher
temperatures in the solar drier increased meat proteolysis; hence
the lower ERV [1]. The alkaline pH of 7.0-7.1 also indicates
excessive proteolysis and breakdown of amino acids.

The samples treated with vinegar or HCl were successfully
preserved by drying. After being stored for a week, they showed
no gas formation and no hydrogen sulphide odour, and had ERV
values ranging from 52% to 57%. The surface colour became dark
brown, as would be expected due to the formation of metamyoglobin
from the oxidation of myoglobin. On cooking after elusion of
residual acidity and rehydration, however, the samples treated
with HCl disintegrated and turned into a broth. Vinegar, on the
other hand, did not turn the meat into liquid on cooking, but
made it tender. Further studies with HCl were therefore
discontinued, but vinegar was included in other studies along
with the other bacteriostatic reagents.

Chang'aa was ineffective in achieving chemical stabilization,
as the meat started developing a foul odour within 24 hours of
soaking. Further experimentation with ethanol was therefore also
discontinued.

Treatment with brine, honey, and glycerol

Treatment with brine, honey, or glycerol as a bacteriostatic
agent protected the meat from spoilage while drying (table 2).

TABLE 2. Quality of dried meat treated with brine, honey, or
glycerol, after four weeks' storage (characteristics assessed by
sight and smell)

Treatment

Gas

Odour

Drip

Surface
colour

Frozen







normal

Direct sun
drying

Brine







cooked meat

Honey

+

fermented



dark brown (white spots)

Glycerol







dark brown

Solar
drier

Brine







cooked meat

Honey







dark brown (white spots)

Glycerol







dark brown

Minus () and plus( + ) signs as in table 1.

No changes were noted in terms of gas formation, odour, or
drip formation in the samples treated with brine or glycerol,
which effectively arrested spoilage, whether the meat was dried
directly in the sun or in a solar drier.

The solar drier appeared to be more effective than direct sun
drying for meat treated with honey. Gas was formed and a
fermented odour developed in the sun-dried honey-treated samples.
The spoilage was due to the growth of yeast, which did not occur
with the solar drier. This can be explained by the high
temperatures achieved by the solar drier (> 50 °C) and
perhaps a higher rate of drying, which are not conducive to yeast
growth.

All the samples changed surface colour. Those treated with
brine turned to the colour of cooked meat, while those treated
with honey or glycerol became dark brown.

Weight loss, moisture, and water activity

Samples treated with brine, honey, or glycerol and dried in
the solar drier lost 43%-54% of their weight, compared with
42%-51% for samples treated similarly and dried in the sun (table
3). The differences in weight loss might not appear significant
considering that their measured moisture contents ranged from 12%
to 43% and 18% to 44% respectively for the two drying methods.
However, given the differences in the drying conditions,
especially with respect to temperature and air flow, the weight
loss of the samples dried in the drier may not all be
attributable to moisture loss. As shown in figure 3 (see Figure. 3. Adsorption isotherm for air-dried beef
at 20°C), the water activity in air-dried beef corresponding
to the lowest 12% and 18% moisture content of samples at 20°C
would be approximately 0.63 and 0.75 respectively [8]. However,
the measured lowest water-activity values corresponding to 12%
and 18% moisture level were 0.87 and 0.83 respectively. This
inverse situation confirms that the weight loss in the
drier-dried samples was due to the loss of other materials, most
likely volatile substances, in addition to moisture. This is
likely, considering the high temperatures of 50-70 °C in the
solar drier, where the air flow is more restricted than in open
sun-drying conditions.

Water activity is a more accurate measure for predicting the
ability of microbes to grow in food than moisture content [3].
Glycerol treatment produced the lowest water-activity values,
followed by brine and honey; nevertheless, brine is known to be a
better preservative than glycerol at any given water-activity
level [8].

Many bacteria, including those that cause spoilage and
pathogens, grow most rapidly at water-activity levels in the
range of 0.995-0.980, but only at near-optimum temperatures [3].
Below this range, and especially at nonoptimum temperatures,
microbial growth is severely hindered. Yeasts, especially the
xerophilic types, can grow at a water-activity range as low as
0.85-0.60 [3]. Pathogens can remain viable for long periods under
these conditions but cannot grow. The yeasts that grew in the
honey-treated, sun-dried samples where water activity was 0.91
may have been of the xerophilic types naturally present in honey.
That the yeasts failed to grow in the honey-treated samples dried
in the solar drier, with 0.92 water activity, however, was
probably due to the high temperatures in the drier, which killed
them.

Microbial counts

Table 4 shows very low microbial counts and levels of growth
during three weeks of storage. The counts were well below the
10(6)/cm² considered critical for meat spoilage [2]. The slight
rise in the total viable microbe count in the second week could
be attributed to sampling error and aerobic contamination during
the analysis, since different sets of samples were packaged and
analysed separately after different periods of storage.

TABLE 4. Microbiological status of dried meat after one, two,
and three weeks of storage

Treatment

Colony-forming units (cfu) per gram

Total viable

Yeasts and moulds

Lipolytic

1

2

3

1

2

3

1

2

3

Brine(20%)

12

15

ND

12

7

ND

4

3

ND

Honey

100%

300

230

ND

300

300

ND

ND

ND

ND

75%

300

29

30.177

300

29

30.177

ND

10

ND

Glycerol

16

78

ND

ND

ND

ND

12

20

ND

Vinegar

14

ND

ND

ND

ND

2

2

ND

ND

1, 2, and 3 in the column headings indicate weeks of
storage.
ND= not detected.

However, when honey diluted with 25% water was used, a step
aimed at reducing the cost of the honey, the total viable count,
mainly yeasts, increased to a high level of about 10(7)/g toward
the third week of storage. As already noted, these yeasts are
likely to be the natural xerophilic types in honey. Their uneven
inoculation from honey onto the meat cut for experimentation
could account for the difference between the counts in weeks 1
and 2.

Very low lipolytic counts were detected, and they showed no
evidence of growth during storage.

Other measurements

The ERV values of the samples could not assist in comparing
the effectiveness of direct sun drying and the solar drier, as
the sun-dried samples treated with brine had much lower ERV
values than those dried in the drier, while the reverse was true
for the samples treated with honey or glycerol.

Samples dried in the solar drier had relatively lower
rehydration values and poorer rehydration properties than those
dried directly in the sun.

Neither pH nor the performance of the solar drier over direct
sun drying could assist in predicting any change due to spoilage.

Organoleptic evaluation

Samples treated with 10% brine, 100% honey, glycerol, and
vinegarall dried in the solar drierand frozen meat
were evaluated by nine panellists (table 5). The data were
subjected to a two-way analysis of variance to test for the
consistency of the panellists and the treatments. Both variables
were significant at p <.01 using the F test. Separation of the
panellists into consistent groups by Duncan's multiplerange test
showed that one panellist consistently scored the meat higher
than the others. Accordingly, that person's data were omitted. On
further analysis of the remaining data, the treatments still had
significantly different scores.

TABLE 5. Organoleptic scores of cooked samples of preserved
meat

Treatment

Average

score

Acceptance

rank

Brine (10%)

2.50c

4

Honey (100%)

2.04c

5

Glycerol

2.73b

3

Vinegar

3.00b

2

Frozen

4.63a

1

Data based on eight panellists.
Scores with different superscripts are significantly
different at p < .01.

According to Duncan's multiple-range test, the frozen meat was
the best, followed by the vinegar and glycerol-treated samples,
which were about equally well accepted. The brine- and
honey-treated samples were also accepted equally but ranked last.
As noted, vinegar had the effect of tenderizing meat. Honey, on
the other hand, imparted an unusual fermented off-flavour, which
could explain its low score. The major problem with all the
treated samples compared with frozen meat was a loss of meaty
flavour.

Beef cuts can be preserved equally well using a solar drier or
by direct sun drying, provided they are protected from microbial
and biochemical deterioration with bacteriostatic chemicals,
particularly those that lower water activity. Vinegar, brine, and
glycerol were equally effective in protecting the meats, but
brine and vinegar are more cost effective than glycerol. The
preserved meats tend to lose the meaty flavour that is preserved
in frozen meat, a subject for further investigation.

The authors thank the Food and Agriculture Organization of the
United Nations, which provided funds for the research.
Appreciation is also extended to Jane Njenga of the Department of
Food Technology and Nutrition of the University of Nairobi, who
carried out most of the analyses and experiments.